1. Field of the Invention
The invention relates to a semiconductor device, and in particular to a semiconductor device having an inductor.
2. Description of the Related Art
Many digital/analog devices and circuits have been successfully applied to semiconductor integrated circuits. Such devices may include passive components, such as resistors, capacitors, or inductors. The typical semiconductor integrated circuit includes a silicon substrate. One or more dielectric layers are disposed on the substrate, and one or more metal layers are disposed in the dielectric layers. The metal layers may be employed to form on-chip elements, such as on-chip inductors, by the current semiconductor technologies.
The on-chip inductor is formed on a substrate and includes a metal layer and an interconnect structure. The metal layer surrounds from the outside to the inside with respect to a center region, and is embedded in an upper insulating layer on the substrate. Moreover, the metal layer closest to the center region further surrounds from the inside to the outside, and is embedded in the upper insulating layer on the substrate. The interconnect structure includes an upper connection layer embedded in the upper insulating layer, and first conductive plugs and a lower connection layer embedded in a lower insulating layer. A current path is created by the metal layer, the first conductive plugs, and the upper and lower connection layers so as to electrically connect to the internal or external circuits of the chip. Two ends of the metal layer are at the outermost coil thereof and each of the ends connects to an extending portion. The two extending portions are parallel to each other and may be connected to various circuit elements. Moreover, the aforementioned on-chip inductor may further include a branch structure. The branch structure is connected to the innermost coil of the metal layer through a second conductive plug embedded in the lower insulating layer. Particularly, the extending direction of the branch structure is perpendicular to that of the two extending portions at the two ends of the metal layer as viewed from a plan view of the on-chip inductor.
An equivalent circuit composed of the two extending portions and the branch structure of the aforementioned on-chip inductor is a T-coil. Circuit parameters of the T-coil include a first inductance, a second inductance and a coupling parameter. The first inductance value and second inductance value are proportional to wiring lengths. For example, an inductance value is determined by the wiring length from one end of the outermost coil of the metal layer to the connecting location of the innermost coil and the branch structure, and another inductance value is determined by the wiring length from another end of the outermost coil to the location of the branch structure. Moreover, the coupling parameter value is varied with the first inductance value and second inductance value. The first inductance value, the second inductance value and the coupling parameter value are usually adjusted by changing the connecting location of the innermost coil of the metal layer and the branch structure.
However, since the connecting location of the innermost coil of the metal layer and the branch structure is limited within a range of a side length of the innermost coil of the metal layer, the structure of the conventional on-chip inductor makes it difficult to meet various circuit-design demands. Moreover, since the first inductance value, the second inductance value and the coupling parameter value are all varied with the location of the branch structure, it is difficult to adjust the circuit parameters of the on-chip inductor.
Thus, there exists a need in the art for development of a semiconductor device having an inductor capable of mitigating or eliminating the aforementioned problems.